Civil infrastructure construction and maintenance represent a large societal investment. Despite being the lifeline of commerce, civil infrastructure has scarcely benefited from the latest advances in sensor technologies. Roadway work zones used for assessment and repair are a major source of traffic congestion, which results in lost productivity and wasted fuel.
Bridge deck and pavement deterioration frequently takes place below the surface and cannot be evaluated by visual means. Concrete deck deterioration includes delamination arising from chloride-induced rebar corrosion, cracking caused by alkali silica reaction (ASR), and cracking caused by overloading or excessive vibration. Pavement deteriorates due to internal moisture damage, debonding, and loss of subsurface support. Reinforced concrete (RC) or prestressed concrete (PC) bridge decks are often overlaid with an asphalt concrete or Portland cement concrete. The presence of the overlay makes it more difficult to detect the subsurface deterioration, and the overlay can also develop damage due to debonding. Pavement layers are subjected to extensive abrasion and deterioration from service loading (e.g., traffic) and environmental attacks (e.g., freeze-thaw, rain, road salts), and thus are subject to deterioration.
Common types of roadway damage are transverse cracks, longitudinal cracks, tracking, corrugation, potholes, delamination, and seepage. Transverse cracks occur more often than longitudinal cracks and can start with a fine crack of less than 0.5 mm in width and of less than 2 cm in depth. Such cracks are hardly visible when it is sunny, but are visible after rain due to the vaporization of the surface water that leaves water in the cracks. Small cracks need to be treated to prevent them from developing into larger cracks. Large cracks often have widths of more than 1 mm, depths of 5 cm, and run meters in length. If large cracks are not sealed, delamination and scaling will follow. If the adhesion between pavement and concrete deck decreases, the overlay may debond from deck's top surface. The loss of adhesion may be caused by seepage from cracks or potholes. Local debonding may span only several square centimeters and can be difficult to detect because the pavement surface remains intact. Large area delaminations may develop into large cracks at the pavement surface and eventually cause large potholes and loss of pavement. Feedback effects can complicate and accelerate damage progression. Cracks and potholes are often accompanied by seepage. Water enters into the overlay through cracks. The adhesion between asphalt and concrete deck is extremely vulnerable to water penetration. Water within cracks of a pavement will stay and seep. This is most harmful to asphalt pavement.
Traditional bridge deck inspection methods, such as chain drag, half-cell potentials, and chloride contents are slow, require closures, and are often not effective. Higher speed technologies such as ground penetrating radar (GPR), infrared thermography, and scanning impact-echo have been developed and used to some extent by highway agencies to meet their needs for bridge deck condition assessment. However, these technologies suffer from the need for traffic closures and insufficient spatial data coverage, which has reduced their acceptance and reliability. Thus, there remains a need for improved road and bridge deck inspection methods and devices using sensor technology.